1. Field of the Invention
The present invention relates to a semiconductor optical modulator.
2. Description of the Related Art
Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2005-99387) describes a semiconductor optical modulator. The semiconductor optical modulator includes a single p-n junction in a cladding layer, which is disposed on the outside of a core layer.
The semiconductor optical modulator described in Patent Literature 1 includes a semiconductor optical waveguide having a nin-type heterostructure.
In Patent Literature 1, to prevent carriers generated by optical absorption in the core layer of the optical modulator from being trapped at a heterointerface, an intermediate cladding layer is disposed on the top and bottom of the core layer of the optical modulator. These two intermediate cladding layers on opposite sides of the core layer are made of InGaAlAs having larger bandgap energy than that of the core layer. An InGaAlAs cladding layer having larger bandgap energy than that of the intermediate cladding layers is disposed on the top of one of the intermediate cladding layers. An InGaAlAs cladding layer having larger bandgap energy than the intermediate cladding layers is disposed on the bottom of the other intermediate cladding layer.